The problem is the human condition is we believe people and sources that we trust, and we discredit sources that we distrust.
Even with the smartest people, they are going to have a belief bias based on information they trust. To change a persons mind they will often need need that trusted source to explain why it is wrong, or for events that would loose your trust into that source.
For many people a pastor or other religious person of some clout is in a position of being a trustworthy fellow. And they would be able to push a message that people would believe (even from some rather intelligent people) that is overall just nonsense, and even contradictory to the tenants of the religion.
"Ah-ha!" says an Atheist, "because I don't trust religious folks then I am immune to such nonsense, my beliefs are based by empirical facts."
Well no, they are just as irrational as the religious person, but they are just trusting different sources. Say a political group (who may have some good ideas, but also tied in with crazy ones), marketing from companies, misinformation/FUD, or from your favorite news source, who makes those other guys seem like insane idiots.
There is a lot of so called "science" reporting, which is loosely around a scientific study, but often just a hypothesis at best, that a group of people are getting paid to study, however being from a trusted science source you may trust the message it is trying to convey. Even if it ultimately wrong.